From 3f74306ac84cf7f2da2fdc87014fc455f5e67bad Mon Sep 17 00:00:00 2001 From: Rob Gardner Date: Tue, 22 Dec 2015 21:16:06 -0700 Subject: [PATCH] sparc64: Ensure perf can access user stacks When an interrupt (such as a perf counter interrupt) is delivered while executing in user space, the trap entry code puts ASI_AIUS in %asi so that copy_from_user() and copy_to_user() will access the correct memory. But if a perf counter interrupt is delivered while the cpu is already executing in kernel space, then the trap entry code will put ASI_P in %asi, and this will prevent copy_from_user() from reading any useful stack data in either of the perf_callchain_user_X functions, and thus no user callgraph data will be collected for this sample period. An additional problem is that a fault is guaranteed to occur, and though it will be silently covered up, it wastes time and could perturb state. In perf_callchain_user(), we ensure that %asi contains ASI_AIUS because we know for a fact that the subsequent calls to copy_from_user() are intended to read the user's stack. [ Use get_fs()/set_fs() -DaveM ] Signed-off-by: Rob Gardner Signed-off-by: Dave Aldridge Signed-off-by: David S. Miller --- arch/sparc/kernel/perf_event.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/sparc/kernel/perf_event.c b/arch/sparc/kernel/perf_event.c index 3091267c5cc3..b1144d6acffe 100644 --- a/arch/sparc/kernel/perf_event.c +++ b/arch/sparc/kernel/perf_event.c @@ -1828,11 +1828,16 @@ static void perf_callchain_user_32(struct perf_callchain_entry *entry, void perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs) { + mm_segment_t old_fs; + perf_callchain_store(entry, regs->tpc); if (!current->mm) return; + old_fs = get_fs(); + set_fs(USER_DS); + flushw_user(); pagefault_disable(); @@ -1843,4 +1848,6 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs) perf_callchain_user_64(entry, regs); pagefault_enable(); + + set_fs(old_fs); } -- 2.30.2